Two adaptive notch filters (ANFs) based on the double integrators (ANF _R ) and the unbalanced synchronous reference frame control (ANF _dq ) were applied to the bus voltage control of a single-phase grid-connected inverter. This article also proposes a non-invasive prognostic function for the degradation of the bus capacitance using the difference between the bus ripple amplitudes estimated from the ANFs and the dq -axes currents with the nominal bus capacitance. The ANF _R , ANF _dq , and conventional notch filters (NFs) were experimentally validated with a 220-V, 50-Hz, 2.5-kW two-stage inverter. The bus voltage control schemes using the three NFs tuned at a fast bandwidth of 30 Hz exhibited identical performance with the grid current harmonics complied with the IEEE 1547 standard. Moreover, the ANF _R and ANF _dq control schemes maintain low current distortion with a variable grid frequency of 45–55 Hz. The capacitance degradation prognostic function accurately responded to a 27% reduction in the bus capacitance. Considering the control performance and computational effort, the ANF _R is suitable for bus voltage control of the single-phase inverter.

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